June 2016

Region-specific foot pain doesn’t always match pressures, forces

Gait compensation may play role

By Emily Delzell

The location of foot pain doesn’t always correspond with elevated plantar pressures and abnormal forces, which suggests the availability of region-specific compensatory gait mechanisms may play a role, according to recent research using Framingham Foot Study data.

Investigators included 3158 Framingham participants (56.1% women, 6280 feet) aged 66.2 ±10.5 years. Participants walked barefoot at a self-selected pace across mats that captured pressure and force data, which were calculated for four regions: the toes, forefoot, midfoot, and rearfoot. Participants self-reported specific foot regions as having pain, aching, or stiffness on most days or no pain.

Investigators grouped feet by pain region: toe pain only (TPO); forefoot pain only; midfoot pain only (MPO); rearfoot pain only (RPO); pain in two regions; pain in three or more regions; and no foot pain. Patients reported regional foot pain in 1520 feet (24.2%), with the forefoot the most common location of pain (12.1%). Patients with RPO were younger than those without pain, and women were more likely than men to have TPO, FPO, and pain in multiple foot regions.

The findings underscore the need for a holistic approach to orthotic design, rather than always offloading areas of high pressure or force.

Investigators found associations between pain and abnormal pressure and forces only in participants with rearfoot and midfoot pain. Compared with pain-free feet, patients with RPO had significantly lower rearfoot peak pressure (-6.1%) and rearfoot maximum vertical force (-5.1%). At peak vertical loading, RPO feet had significantly lower rearfoot force (3.1%) and higher forefoot force (2.8%). Feet with MPO didn’t have higher pressure in the pain region than pain-free feet, but toe pressure was 6.1% higher, and these participants had greater maximum vertical force at the forefoot (3%) and midfoot (24.1%) and 3.5% higher midfoot force at peak vertical loading than those without pain.

The lower forces found with rearfoot pain may result from participants slowing their walking speed, having reduced ankle dorsiflexion (not evaluated in this study), or both, said Jody Riskowski, PhD, a biomechanical researcher at Glasgow Caledonian University in the UK and lead author of the study, which was published in October by the Journals of Gerontology: Medical Sciences.

“Based on some prior Framingham work, the more likely reason is reduced gait speed,” she said.

In participants with midfoot pain, Riskow­ski and her colleagues identified a number of foot disorders, particularly hammer­toes.

“Hammertoes can reduce toe muscle forces for push-off during gait, and the midfoot will provide greater force, which often leads to greater pressure during walking,” she said. “Notably both regions where we saw associations with regional pain to aberrant forces and pressures were in the proximal foot, where it may be harder for the individual to change gait, given these areas are necessary for the loading phase. Individuals with distal foot pain may use different foot regions for push-off—most likely the midfoot. In the end, the main difference for some pain regions having association with aberrant pressure or forces seems to be the availability of a compensatory mechanism for gait.”

“It’s nice to see this paper confirming what podiatrists often see in clinical practice,” said Bruce Williams, DPM, director of Gait Analysis Studies at Weil Foot-Ankle & Orthopedic Institute in Chicago, who reviewed the study for LER: Foot Health. “Often, where patients hurt isn’t where the problem is, and where the problem is isn’t where it hurts.”

As in the study, Williams is more likely to see increased region-specific forces associated with midfoot pain than rearfoot pain, he said.

“Quite often what I’ll see in patients who have heel pain, for example, is that they tend to avoid that area, so you see the increase overall in vertical forces,” he said. “With forefoot pain, I see a lot of high pressures, especially under the central metatarsals when patients have a neuroma or metatarsalgia symptoms; that pain often will be consistent because pressure will light up early in that area.”

Riskowski feels the study underscores the need for a holistic approach to orthotic design.

“I think there often is an assumption that we should offload areas of high pressure with orthotics. For many populations, particularly those with diabetes or peripheral neuropathy, it is paramount to reduce the risk for ulcers,” she said. “But another important consideration should be evaluating the effects of wearing an orthotic versus not wearing the orthotic with respect to joint movements at the ankles, knees, and hips. Several studies suggest aberrant foot mechanics are associated with greater risk of pain in the ankles, knees, and hips, and the role of the orthotics should be to restore and/or promote a more effective and natural foot function to keep all joints happy and healthy, not just to offload high forces at the foot.”